Study of seawater biofiltration by measuring adenosine triphosphate (ATP) and
turbidity
F. Xavier Simon1, Elisabet Rudé1, Joan Llorens1, Sylvie Baig2
1
Department of Chemical Engineering, University of Barcelona, C/ Martí i Franquès 1, 08028
Barcelona, Spain
2
Degrémont SA, 183 avenue du 18 juin 1940, 92508 Rueil-Malmaison cedex, France
Abstract
In the present study, we examined seawater biofiltration in terms of adenosine
triphosphate (ATP) and turbidity. A pilot biofilter continuously fed with fresh
seawater reduced both turbidity and biological activity measured by ATP.
Experiments operated with an empty bed contact time (EBCT) of between 2 and 14
min resulted in cellular ATP removals of 32% to 60% and turbidity removals of 38%
to 75%. Analysis of the water from backwashing the biofilter revealed that the first
half of the biofilter concentrated around 80% of the active biomass and colloidal
material that produces turbidity. By reducing the EBCT, the biological activity moved
from the first part of the biofilter to the end. Balances of cellular ATP and turbidity
between consecutive backwashings indicated that the biological activity generated in
the biofilter represented more than 90% of the detached cellular ATP. In contrast, the
trapped ATP was less than 10% of the overall cellular ATP detached during the
backwashing process. Furthermore, the biological activity generated in the biofilter
seemed to be more dependent on the elapsed time than the volume filtered. In
contrast, the turbidity trapped in the biofilter was proportional to the volume filtered,
although a slightly higher amount of turbidity was found in the backwashing water;
this was probably due to attrition of the bed medium. Finally, no correlations were
found between turbidity and ATP, indicating that the two parameters focus on
different matter. This suggests that turbidity should not be used as an alternative to
cellular concentration.
Keywords: biofilter; biofiltration; seawater; adenosine triphosphate (ATP); turbidity
* To whom correspondence should be addressed.
E-mail: [email protected]
Tel: +34 934020155; Fax: +34 934021291
1
1. Introduction
Increasing water demand has led to the development of new strategies for using
existing water resources. At the same time, technological developments have
improved water treatment processes to guarantee and maximize the production of
high-quality water for different purposes. From a general point of view, biofiltration
uses living material to capture and biologically degrade pollutants. The biofiltration of
surface water is a common operation that has been widely and successfully used in
water treatment for the last 20 years (Huck et al., 1994; Urfer et al., 1997).
Biofiltration is used as a pretreatment process in membrane filtration (Persson et al.,
2006; Chinu et al., 2009) and is installed downstream from advanced oxidation
processes (e.g. ozonation) to reduce ozonation by-products (Servais et al., 1994;
Carlson and Amy, 1997; Ahmad and Amirtharajah, 1998). Another purpose of
biofiltration is consumption of the biodegradable fraction of natural organic matter
(NOM) in order to prevent downstream operational problems such as regrowth in
pipelines (Servais et al., 1994; Huck et al., 1994; Urfer et al., 1997; Ahmad et al.,
1998; Ahmad and Amirtharajah, 1998; Persson et al., 2006; Emelko et al., 2006).
Furthermore, good efficiency in turbidity removal can also be attributed to
biofiltration since it can act as a conventional physical filter, which results in
acceptable filtration performances (Wang et al., 1995; Urfer et al., 1997; Ahmad and
Amirtharajah, 1998; Emelko et al., 2006).
Biofilters consist of a packed bed, which can be made of different porous materials,
with an attached biomass that forms a biofilm on the surface (Huck et al., 1994). The
filter medium provides the surface for cell attachment (Wang et al., 1995). Attached
growth has several advantages over suspended growth, and some of these were
reviewed by Cohen (2001). In a biofilter, the biomass grows at the expense of the
biodegradable matter present in the medium, leaving depleted water downstream with
only the more refractory substances that should not interfere in subsequent processes.
Assuming that temperature is barely controlled in industrialized biofilters, the process
variables in biofilters are commonly the empty bed contact time (EBCT), the
hydraulic loading rate (HLR) and the intensity and frequency of the backwashings
(BW) (Liu et al., 2001; Miltner et al., 1995; Urfer et al., 1997; Persson et al., 2006).
Periodic backwashings of the bed are necessary in order to maintain the performance
of the biofilter by removing the biomass that has built up and the captured suspended
2
solids (Ahmad and Amirtharajah, 1998). Different types of filter media have been
used, e.g. granulated activated carbon (GAC), expanded clay (EC).
Many studies of freshwater biofiltration can be found in the literature; unfortunately,
to the best of our knowledge few papers concerning seawater biofiltration are
available. A summary of seawater biofiltration studies found in the literature are
shown in Table 1. Note that, despite anthracite and sand in slow-filtration mode could
also be considered biofilters (Wang et al., 1995) they are not taken into account.
Table 1
In this work, we study biofiltration as a process for reducing colloidal matter and the
biological activity of seawater. For this purpose, different EBCTs, between 14 and 2
min, corresponding to hydraulic loading rates between 6 and 25 m h-1, were tested in a
pilot-scale biofilter. The biological activity was evaluated by measuring adenosine
triphosphate (ATP) and the colloidal material by measuring turbidity. The biological
activity and colloids trapped, accumulated and generated during the continuous
biofiltration operation were considered.
2. Materials and methods
2.1. Pilot biofilter
A pilot biofilter was installed and operated on the coast of Barcelona, next to the
Barcelona city desalination plant in El Prat de Llobregat. The pilot plant was operated
for one year. The biofilter consisted of two glass columns filled with expanded clay as
a filter medium (columns C-1 and C-2) (see Figure 1). Both columns were connected
and operated in series. Teflon® tubing was used for all streams: inlet, outlet and
interconnections. In order to avoid algal growth, the columns were wrapped in
aluminium foil.
Three sample points were analysed: the seawater inlet (inlet), the outlet of column C-1
(outlet C-1) and the outlet of column C-2 (outlet C-2). Note that the outlet of C-2 is
also referred to as the biofilter effluent. Figure 1 shows a schematic representation of
the pilot biofilter and |
Table gives the characteristics of the packed bed.
Particles of expanded clay, Biolite® L2.7, were used as a packing medium in the
biofilter. This porous material has a high specific area and provides a surface for the
biomass to attach to and grow on.
3
Figure 1
|
Table 2
Seawater was pumped directly from the NW Mediterranean Sea, 2 km offshore and at
a depth of 25 m. Table 3 summarizes the seawater characteristics.
Table 3
More details on seawater characterization and analyses are given elsewhere (Simon et
al., 2011; Simon et al., 2013; Penru et al., 2013).
Biomass acclimation
The colonization and acclimation of the biofilter was performed by filtration of
seawater for several months. An additional biodegradable source of carbon, e.g.
sodium acetate or glucose, was not supplied, as proposed by other authors (Yang et
al., 2001; Visvanathan et al., 2003; Meesters et al., 2003). During the acclimatization
period, dissolved oxygen was measured in the inlet and outlet streams in order to
ensure a steady-state regime prior to the normal biofiltration operation.
Backwashing
Both columns were backwashed separately twice a week. The backwashing process
involved water washing and air scouring (Amirtharajah, 1993; Ahmad and
Amirtharajah, 1998; Emelko et al., 2006). During the backwashing process, the bed
expanded by up to 20-30%. Raw seawater was used as a washing medium and carrier
for the detached biomass, as proposed by other authors (Liu et al., 2001).
ATP and turbidity samples (referred as S1 – S3) were collected during the
backwashing protocol described below:
1. Partial drainage of the water in the column
2. Bed expansion with air (100 m h-1 for 1 min)
3. Water and air washing (water 20 m h-1 | air 100 m h-1 for 3 min), → S1
4. Water washing only (20 m h-1 for 2 min)
5. Repeat 1- 4 → S2 (during water and air washing sampling)
6. Final rinsing (20 m h-1 for 12 min) → S3
4
2.2. Experimental conditions
Different operational conditions were analysed. The EBCT varied from 14 to 1.8 min,
which corresponded to hydraulic rates from 6 to 25 m h-1. Table 4 summarizes the
experimental conditions.
Table 4
2.3. Analytical determinations
All materials used in the analyses were made of glass or Teflon®. These materials
were carefully cleaned before use in order to avoid contamination. Glass material was
first soaked in HCl aqueous solution (10% V/V) for 24 hours and then rinsed with
large amounts of Milli-Q water. After this, the material was covered with aluminium
foil and muffled at 450ºC for 4 hours to remove all remaining traces of organic
compounds. Plastic material was also cleaned and sterilized by autoclave (QM 4000
SA-202X, Quirumed Spain) for 30 min at 121ºC.
Adenosine triphosphate (ATP) determination
ATP measurements were performed to monitor the biomass activity in the seawater
samples during the biofiltration process, but also in the backwashing samples. ATP
(ATPTOTAL) is present in the ecosystem in two forms: cellular ATP (ATPCELL), which
is directly associated with living cells, and free ATP (ATPFREE) dissolved in the media
and not contained in the cells, known as extracellular ATP (Karl, 1980). The ATPCELL
content is proposed as an indicator of active biomass content, since ATP is a
biomolecule present in all active microorganisms (Holm-Hansen and Booth, 1966;
Hammes et al., 2010). In this work ATP CELL content was chosen instead of
heterotrophic plate count (HPC) for measuring active biomass content. Although HPC
and ATP sometimes correlate (Deininger and Lee, 2001; Delahaye et al., 2003; Magic
Knezev and van der Kooij, 2004; Hammes et al., 2010), especially in water with a low
organic content (Veza et al., 2008), using HPC overestimates underestimates the real
content of cells because it measures cultivable cells (Ahmad and Amirtharajah, 1998).
In addition, ATP analysis is less laborious and time-consuming than other methods of
assessing biomass (Velten et al., 2007).
5
ATPTOTAL and ATPFREE were quantified using a BacTiter-GloTM Microbial Cell
Viability Assay (G8231, Promega Biotech Ibérica, Spain) and a GloMax® 20/20
Luminometer (Promega Biotech Ibérica, Spain). Samples were previously filtered
through a 0.22-m filter (to retain bacterial cells) to measure ATPFREE. The ATPCELL
was determined indirectly by subtracting the ATPFREE from the ATPTOTAL, as
described by Equation 1:
ATPCELL = ATPTOTAL – ATPFREE
[1]
Measurements were performed by mixing 100 L of the seawater sample and 100 L
of ATP reagent in an Eppendorf tube. The mixture was agitated in an orbital mixer for
3 min at room temperature, and after 30 s the luminescence signal was recorded and
measured as relative light units (RLU). RLU were converted to ng ATP L-1 using
ATP standard dilutions (A3377, Sigma-Aldrich, USA). All the ATP analyses were
performed in triplicate.
Turbidity
Turbidity was measured using a 2100P Turbidimeter (Hach, USA), in accordance
with the EPA 180.1 method.
Scanning electron microscopy (SEM)
SEM images were taken of the colonized and virgin bed media. The media were fixed
in 2.5% (W/W) of glutaraldehyde (buffered with filtered seawater at 4ºC) for one hour
and then washed to remove residual salt. One per cent of OsO4 in filtered seawater
was then used for post-fixation of the sample. Next, dehydration was carried out by
rinsing with ethanol/water, followed by critical point drying with liquid CO2. Finally,
the samples were sputter-coated with gold before examination with an SEM
microscope (Quanta 200 FEI, XTE 325/D8395) operated at 20 kV.
Fluorescence in situ hybridization (FISH)
The presence of bacteria on the media was proved by fluorescence in situ
hybridization (FISH). Thus, biomass from the backwashing was collected and fixed
with 4% paraformaldehyde (Amann et al., 1990). The oligonucleotide probe EUB338
was used to detect the bacteria domain. Additional details are available at probeBase
6
(Loy et al., 2007). Hybridization was performed at 46ºC for 90 min. EUB338 was 5’
labelled with the dye FLUOS and compared with DAPI staining which is highly
specific of RNA and has also been used to detect microorganisms in seawater
sediments (Llobet-Brossa et al., 1998). Fluorescence signals were recorded with a
confocal microscope (Leica TCS-SPE).
3. Results and Discussion
3.1. SEM and FISH results
Figure 2a and 2b show SEM images of the virgin and colonized filter media,
Biolite®L2.7, which provides porosity with voids and recesses sheltered from fluid
shear forces. Thus, the biofilm can start to grow and develop, as shown in the fully
colonized media. There are clear differences between the colonized and noncolonized media due to the presence of extracellular polymeric substances that are
mainly composed of polysaccharides, but also proteins (Flemming and Wingender,
2001). Furthermore, the overlap of images after DAPI staining (Figures 2c) and
bacteria domain (Figure 2d) obtained by FISH analysis proved the presence of
bacteria populations corresponding to the bacterial domain.
Figure 2
3.2. ATP and turbidity evolution during normal biofiltration
Analyses of the free and total ATP were performed at the inlet stream of the biofilter
and the outlet streams of columns C-1 and C-2. The ATP concentrations obtained
show that some biological activity was retained during the biofiltration process (see
3a). In this work, ATP removals of 45% to 60% were achieved, depending on the
biofiltration conditions. Moreover, the reduction in ATP achieved by column C-1
represented ~80% of the overall removal achieved by the entire biofilter. At least 78 80% of the ATP found in seawater is cellular ATP. Throughout the biofiltration
process, depending on the conditions applied, cellular ATP represented 73 - 82% of
the total ATP. These results indicate that in general both cellular and extracellular
ATP are equally retained by the biofilter. However, despite the above mention, some
ATP detached from the biofilter could be found in the biofilter effluent and then
slightly decrease the retention efficiency.
7
These findings agree with the bacterial reductions found by Persson et al. (2006),
although we measured biological activity instead of the number of bacterial
populations, and they are also in line with Meesters (2003), who found 30- to 40-fold
lower ATP concentrations in biofiltered water than in feed water.
Figure 3b shows the turbidity measured at the inlet and outlet streams of columns C-1
and C-2 in biofiltration processes Exp-1, Exp-2 and Exp-3 (see Table 5). The turbidity
measured in the inlet streams is always low (around 1 NTU) and the turbidity in the
final output streams reaches values of between 0.41 and 0.26 NTU, depending on the
experimental conditions.
Figure 3
Removal of turbidity and cellular ATP compared to the EBCT by columns C-1 and C1 + C-2 is shown in Figure 4. Both turbidity and ATP follow the same pattern. More
than 30% of cellular ATP is removed in an EBCT of less than 2 min. Increasing the
EBCT has a positive effect on ATP removal, with 14 min of biofiltration achieving
removals of around 60%. Turbidity removals of about 40% are reached at an EBCT of
2 min. Finally, a maximum turbidity removal of up to 75% was also obtained with the
highest EBCT of 14 min. These reductions in turbidity are comparable with those
obtained by others (Ahmad and Amirtharajah, 1998; Persson et al., 2005; Chinu et al.,
2009). On the contrary, no correlation was found between these reductions and the
HLR in the studied range of 6 – 25 m h-1.
Figure 4
3.3. ATP and colloidal material balance
A general mass balance is described by Equation 2. ATP and the colloidal material
that gives turbidity were balanced between two consecutive backwashing processes
for the different biofiltration conditions. The ATP or turbidity balance may be useful
for assessing the ATP or turbidity trapped during the biofiltration process (referred to
as I – O in Equation 2) and generated in the biofilter due to biological activity
(referred as G). The ATP and turbidity accumulated due to biofiltration but also
8
generated between two consecutive backwashings in the biofilter can be determined
as E in Equation [2].
Assuming that backwashings were performed in the same way every time,
biofiltration is considered a cyclic process in which the ATP and turbidity at the outlet
of the biofilter are restored after few time of performing the backwashing.
(I – O) + G = E
[2]
I = Input of total ATP and turbidity in seawater influent between 2 consecutive backwashings
O = Output of total ATP and turbidity in BF effluent between 2 consecutive backwashings
G = Generation of total ATP and turbidity into the biofilter between 2 consecutive backwashings
E = Extracted ATP and colloidal material during the backwashing
The ATP and turbidity computed in the global balance in the biofiltration processes
Exp-1, Exp-2 and Exp-3 are shown in Table 5. The Input and Output refer to the
concentrations in the inlet and outlet streams multiplied by the total volume of
seawater treated between two consecutive backwashings. Extracted ATP and turbidity
were calculated as the product of the concentration estimated by the backwashing
samples (S1, S2, and S3, see Section 2.1) and the volume of rinsing water used in the
backwashing. The Generated value was calculated using Equation [2].
Table 5
These balances highlight that the generation of ATP and turbidity is much higher than
the ATP and turbidity retained during the biofiltration operation (I – O). Therefore,
ATP and colloidal material trapped by the biofiltration process is much lower than
that which is detached during the backwashing process despite that some material
from the biofilter are probably detached between the backwashings.
No direct correlation was found between the total quantity of filtered water and the
quantity of ATP detached during the backwashing process (R2 = 0.20). However, a
direct correlation was found between the quantity of filtered water and the turbidity
detached during the backwashing (R2 = 0.96). A possible explanation for this finding
is that the HLR is greater when the amount of filtered water is greater, and therefore
9
the attrition generated in the bed medium increases. From this, we deduce that
backwashing is basically an instrument for removing generated rather than trapped
material.
The contribution of ATP and turbidity detached from columns C-1 and C-2 during the
backwashing are shown in Figure 5. As stated before, column C-1 always contains
much more ATP and colloidal material than C-2, which is in agreement with the
scientific literature (Servais et al., 1994; Persson et al., 2005). Thus, a minimum of
80% of the ATP and 70% of turbidity is found in column C-1. The distribution of
ATP along the biofilter depends on the filtration conditions. Decreasing the EBCT
involves the shift of ATP from the input to the output of the filter, or in other words,
biological activity displacement from column C-1 to C-2.
Figure 5
The measured percentages of ATPCELL in the backwashing waters are shown in Table
6. This percentage of ATPCELL was always higher than that measured in the inlet
seawater. Notice that the cellular ATP of the last water sample from the backwashing
(S3), is close to the raw seawater which is used as rinsing water. As expected, the
results indicate that the active biomass in the biofilter generates cellular ATP. A
comparable percentage of ATPCELL was found in the first and second backwashing
samples (S1 and S2, respectively) for both columns and irrespective the experiment.
On the contrary, the maximum turbidity was found in the first cycle (data not shown).
A possible explanation for this could lie in the biological and non-biological nature of
ATP and turbidity that makes bacteria to adhere to the bed medium more than
colloidal particles (Ahmad and Amirtharajah, 1998).
Table 6
3.4. Cellular ATP and turbidity correlations
All ATP and turbidity results obtained in normal biofiltration and backwashing
processes have been plotted in Figure . The possible correlations between ATP and
turbidity may be interesting from an industrial control point of view (turbidity is a
straightforward measure).
10
Figure 6
The results show a low correlation (R2 = 0.39 – 0.65) between these parameters,
regardless of the concentration range. These findings are in line with those reported
by Ahmad (1998); once again proving that turbidity is not always a good measure of
cell concentration.
4. Conclusions
- The ATPCELL removal by biofiltration reaches 60% at EBCT = 15 min.
Furthermore, EBCT impacts positively but not the HLR in the conditions studied.
- Around 80% of the biofilter activity and colloidal material is concentrated in the
first half of the biofilter.
- ATP generated between consecutive backwashings is by far higher than the
biological activity retained due to biofiltration. Moreover, ATP generated in the is
slightly dependent on EBCT and HLR in the range of the conditions studied.
However, decreasing the EBCT implies an increase in the active volume occupied
by the microorganisms in the biofilter.
- Biological and non-biological particles exhibited different trapping behaviour due
to their nature.
Acknowledgements
The authors are grateful to the Spanish Ministry of Industry (CDTI) for their financial
support within the framework of the Project CENIT: CEN20071039 and also to S.
Lopez from the University of Barcelona and M. Abad and Dr. E. Berdalet from
CMIMA-CSIC for their kind assistance.
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16
C-2
backwashing
SW effluent
C-1
backwashing
SW effluent
dc = 100 mm
C-1
BF
effluent
C-2
SW
inffluent
air
Figure 3. Schematic representation of the biofiltration facility
17
(a)
(c)
(b)
(d)
5 m
5 m
Figure 4. (a) SEM micrograph of virgin media; (b) colonized media; (c) confocal
micrograph after DAPI staining (d) confocal micrograph of bacteria domain after
labelling with EUB338 FISH probe
18
Figure 3. (a) Concentrations of ATPCELL and ATPTOTAL and (b) turbidity in the inlet
stream and outlet streams of columns C-1 and C-2 in biofiltration process: Exp - 1,
Exp – 2, and Exp - 3 (see Table 4).
(vertical bars correspond to std. dev.)
19
Figure 4. Removals of turbidity and ATPCELL vs. EBCT
20
Figure 5. Relative percentage of ATP and turbidity detached in columns C-1 and C-2
during the backwashings. (Note that % C-1 + % C-2 = 100%)
21
(a)
(b)
Figure 6. Correlations of ATPCELL vs. turbidity: (a) biofiltration
process; (b) backwashing process.
22
Table 2. Literature on seawater biofiltration
Biofiltration conditions
Seawater quality
*
GAC
EBCT = 60 – 15 min
HLR = n.d.
- DOC = 3 – 15 mg L
*
modified by artificial additions
of sodium acetate
GAC
EBCT = 10 – 5 min
anthracite
HLR = 5 – 10 m h-1
- Turb. = 0.5 – 0.7 NTU
- TDS = 35 g L
-1
- Turb. = 0.68
HLR = 5 – 10 m h-1
- Conduct. = 39.9 mS cm-1
- DOC = 0.96 mg L-1
HLR = 5 – 10 m h
-1
- Biofiltration + MF prior to RO improved 300% RO permeate flux
Visvanathan et al., 2003
- Turb. = 0.2 – 0.3 NTU
Chinu et al., 2009
- DOC removal > 60% (especially LMW organics)
EBCT = 11 – 5 min
EBCT = 11 – 6 min
- ~100% removal of biodegradable DOC
- RO flux decline faster when no pre-treatment was provided
- DOC = 1.85 mg L-1
EC
Reference
- MFI outlet = 10 s L-2 for both biofilters
- pH = 8.10
- pH = 8.03
GAC
Main results
-1
- BOD7 = 1.11 mg L
-1
-1
- AOC outlet = 0.6 µg-C L-1
- TEP outlet = 5.3 µg-C L
Naidu et al., 2013
-1
- DOC removal = 6% (LMW neutrals 33% and biopolymers 17%)
- BOD7 removal = 15%
- A254 = 0.67 m
- ATP removal = 60%
- Turb. = 1.06 NTU
- 94% of biofilm formation capacity reduction
Simon et al., 2013
A254 = Absorbance at λ = 254 nm; ATP = Adenosine triphosphate; BOD7 = Biochemical oxygen demand at 7 days; Conduct. = Conductivity; DOC = Dissolved organic
carbon; EBCT = Empty bed contact time; EC = Expanded clay; GAC = Granulated activated carbon; HLR = Hydraulic loading rate; LMW = Low molecular weight; MF =
Microfiltration; MFI = Modified fouling index; RO = Reverse osmosis; TEP = Transparent exopolymer particles; TDS = Total dissolved solids; Turb. = Turbidity; n.d. = no
data.
23
Table 3. Features of the packed bed
Parameter*
Units
Value
Height of the bed
cm
75
Diameter of the bed
cm
10
Ratio height/diameter
-
7.5
Bed volume
L
6
Porosity
-
0.4
m-1
1333
kg m-3
730 – 900
Interfacial area
Bulk density

Both columns (C-1 and C-2) have the same characteristics
24
Table 3. Seawater quality
Parameter
Units
Value
pH
-
8.2
Tubidity
NTU
1.03 ± 0.28
TDS
g NaCl L-1
32.5 ± 0.6
Conductivity
mS cm-1
57.4 ± 0.4
BOD7
mg O2 L
-1
1.57 ± 0.56
DOC
mg C L-1
0.78 ± 0.10
A254
m-1
0.56 ± 0.06
Algae
cells mL-1
264 ± 120
SDI15
% min-1
7.5 ± 6.2
T
ºC
17 ± 3
TDS: Total dissolved solids; BOD7: Biochemical Oxygen Demand at 7 days; DOC: Dissolved Organic Carbon; A254: UV absorbance at λ = 254 nm; SDI15: Silt Density Index
at 15 min; T: Temperature
25
Table 4. Operational conditions in the biofiltration process
Flow rate
HLR
EBCT*
[L h-1]
[m h-1]
[min]
Exp - 1
50
6.4
7.0 + 7.0 = 14
Exp - 2
100
12.7
3.5 + 3.5 = 7.0
Exp - 3
200
25.5
1.8 + 1.8 = 3.6
Name
*
EBCTC-1 + EBCTC-2 = EBCTBF
26
Table 5. ATPTOTAL and turbidity computed in the global balance in biofiltration process: Exp - 1, Exp – 2, and Exp - 3. The Input and Output
correspond to the concentrations in the inlet and outlet streams multiplied by the total volume of water treated between two consecutive
backwashings. ATP and turbidity Extracted were calculated as the product of the concentration by the volume of water used in the backwashing.
The Generated was calculated using Equation [2].
EBCT
Treated water
[min]
[ L × 10-3]
Name
Exp - 1
7 + 7 = 14
4.2
Exp - 2
3.5 + 3.5 = 7
8.4
Exp - 3
1.8 + 1.8 = 3.6
17
INPUT - OUTPUT
EXTRACTED
GENERATED
ATPTOTAL [g ATP]
ATPTOTAL [g ATP]
ATPTOTAL [g ATP]
Turb × 10-3 [NTU L]
Turb × 10-3 [NTU L]
Turb × 10-3 [NTU L]
197
6460
6262
3.3
368
364
435
5559
5123
5.4
1007
1002
709
7421
6712
11.0
1635
1624
27
1
2
Table 6. Percentage of ATPCELL in the backwashing water samples (more information regarding water samples: S1, S2, and S3 can be found in
Section 2.1)
% ATPCELL C-1
% ATPCELL C-2
Name
S1
S2
S3
S1
S2
S3
Exp - 1
95
97
87
94
96
88
Exp - 2
95
97
83
95
96
83
Exp - 3
95
97
90
93
95
92
3
4
28